Hereditary factors play a significant role in the etiology of autism. In addition to autism, abnormalities which are milder, but qualitatively similar to behaviors which define autism (i.e, particular personality, language and cognitive characteristics, and psychiatric disorders), have been shown to aggregate in relatives of autistic individuals. Clarification of the boundaries of phenotypic expression of the underlying genetic liability to autism is a critical preliminary step to further genetic analyses of this disorder. In addition, the finding that social deficits in the relatives of autistic probands, evident in measures of both personality and language, may be biologically-based and etiologically-related to particular cognitive disabilities and psychiatric disorders, is of importance beyond the significance these findings have for understanding the etiology of autism. This is an application for a Scientist Development Award for Clinicians. During the award period, the candidate proposes an organized program of training and supervised research. Training will focus on learning to assess and measure behaviors (i.e., language, personality and cognitive) hypothesized to define a "lesser variant" in autism and to develop a critical fund of knowledge in quantitative, medical and molecular genetics for examining the role of genetic factors in complex childhood neuropsychiatric disorders. The specific aims of the research portion of this award include: 1) estimation of the frequency of disorders that may be genetically associated with autism in first-degree relatives of autistic and Down syndrome probands and 2) definition of the characteristics of a "lesser variant" in autism for use in future genetic studies of this disorder by investigating the pattern of disorders among first-degree autism relatives. A variety of behavioral measures will be used to assess the first-degree relatives of autistic probands from multiple-incidence autism families and Down syndrome probands, in a case/control family study.